High-power industrial laser systems generally produce beams having output powers in the range of several hundreds of Watts to several kW. It is often desirable to deliver the laser power to a processing head or work piece via an optical fiber. Laser systems that can be coupled into an optical fiber for delivery include fiber lasers, disk lasers, and diode- or lamp-pumped solid-state lasers (e.g., Nd:YAG). In these systems, the desired optical power is guided in the fiber core, but some power may also be present in the fiber cladding; this cladding light is undesirable because it can cause excessive heating of or damage to downstream components or optics, or it may otherwise interfere with work piece processing.
In typical fiber laser systems a signal beam is created in an active fiber that includes a rare-earth doped optical fiber core by delivering a pump beam to a cladding of the active fiber at a pump wavelength that is shorter than a signal beam wavelength. At the output of the fiber laser, cladding light may consist of unabsorbed pump light and signal light that has escaped from the core. For both fiber lasers and other lasers, cladding light may be introduced into a beam delivery fiber if launching of the laser beam couples some of the light into the cladding rather than the core. A processing beam directed to a target or work piece can experience reflection or scattering and can become back-coupled into the beam delivery fiber. This back-coupled light can be coupled into both the active or beam delivery fiber core and cladding, and can destabilize, damage, or otherwise interfere with the laser system.
Accordingly, systems that can remove and monitor both forward-propagating and backward-propagating cladding light and backward-propagating core light are needed, particularly to protect against high-power back-reflections.